The term "abnormal tissue" as used herein refers to all forms of tissues which have undergone malignant induction such that these tissues may eventually show loss of growth control which is frequently referred to as cancerous or tumorous growth. The detection of the presence of such abnormal tissues is often made difficult because they are located within the body so that until discomfort or other symptoms are experienced by the individual, the existence of the abnormal tissues may not even be suspected. Additionally, procedures for early detection can be so expensive and complex as to make their use restricted. Therefore, it would be highly advantageous to be able to detect quickly and simply the presence of abnormal tissue or ideally the eventuality of abnormal tissue growth within a body cavity of the host, for example, and preferably the technique should be minimally invasive.
Many forms of cancers or tumors require extended periods of time to achieve a size detectable or injurious to the host, and in some cases this may take many years. Treatment at the present time is considerably more effective when the abnormal tissues are in their early phases and long before they have achieved growth sufficient to cause discomfort or produce symptoms. It would, therefore, also be advantageous to be able to detect the presence of abnormal tissues in their early phases or to detect the tendency for tissues to become abnormal.
Several research efforts have been directed toward discovering the relationship between the electrical impedance of biological tissue and its condition or health. For example, U.S. Pat. No. 3,949,736 discloses that the impedance of biological tissues can provide a useful indication as to whether tissues are healthy or diseased. Specifically, this patent suggests that changes in impedance of biological tissues can be used as a technique for diagnosis of certain carcinomas. According to this patented technique, a low level electric current is passed through the investigated tissue with measurement of the voltage drop across the tissue providing an indirect indication of the overall tissue impedance (i.e., resistance and capacitance). Also, according to this patent, increase in the impedance of the tissue is associated with an abnormal condition of the cells composing the tissue and indicative of a tumor, carcinoma, or other abnormal biological condition of the tissue.